Method and apparatus for fabricating gaseous discharge devices



A. D. WHITE METHOD AND APPARATUS FOR FABRICATING March 4, 1958 GASEOUS DISCHARGE DEVICES Flled March 24, 1955 BREAKDOWN VOLTAGE SUPPLY INVENTOR A. 0. WHITE 81/ I aqmk ATTORNF V United States Fatent G Inn! DIETHOD AND APPARATUS FOR FABRICATING GASEOUS DISCHARGE DEVICES Alan D. White, Plainiield, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, i(., a corporation of New York Application March 24, 1955, Serial No. 4%,391

13 Claims. (Cl. 316-1) This invention relates to gaseous discharge devices and more particularly to methods and apparatus for fabricating such devices.

When gaseous discharge devices are utilized as switching elements in switching networks, as that described in Bruce-Straube Patent 2,684,405, July 20, 1954, the accurate determination of the breakdown voltage of the device becomes of considerable importance. If a tube is operated at the pd minimum of the Paschen curve, generally referred to Ethe Paschen minimum, then the breakdown voltage is not greatly varied by changes in distance or pressure. However, when a device is operated at the Paschen minimum the breakdown voltage is also a minimum. This decreases the margin between the breakdown and sustaining voltages, limiting the number of such devices that may be employed in a switching network without erroneous breakdown of a device due to the eumulative sustaining voltages of other devices applied across it.

It is therefore desirable to operate a gaseous discharge device at other than the Paschen minimum in order to increase this margin between the sustain and breakdown voltages. However, it is still very desirable that the breakdown voltage should be a predetermined value which is constant for all the devices in the network. It therefore becomes important that the initial determination of the anode-to-cathode spacing be made exceedingly accurate.

Priorly the anode-to-cathode gap spacing has been determined by various methods, mainly mechanical in nature, relying on the use of accurate and elaborate jigging fixtures or on the skill of trained technicians to make adjustments by eye using various optical arrangements. All of these methods are complicated, require trained personnel to accomplish, and are susceptible to errors in the determination of the final gap spacing. Further, even though the initial spacing be accurately determined by any or" these methods, the breakdown voltage may still vary between diflerent devices with the same spacing due to slight variations in the initial filling pressure, which is very difficult to control during the manufacture of large numbers of gaseous discharge devices.

It is a general object of this invention to attain accurate adjustment of the critical anode-to-cathode spacing in a gaseous discharge device.

Further objects of this invention include enabling an accurate anode-to-cathode spacing to be attained without the employment of mechanical jigs or optical measurements, attaining the desired spacing automatically to dispense with the necessity of employing trained personnel to determine the spacing, and determining the spacing after the device has been sealed ofi.

Thus it is an object of this invention to provide an improved method for accurately determning the anodeto-cathode spacing of a gaseous discharge device.

It is still another object of this invention to provide Patented Mar. 4, H953 apparatus for automatically determining and checking the anode-to-cathode spacing in a gaseous discharge device.

It is a further object of this invention to enable the attainment of an accurately predetermined breakdown voltage between the anode and cathode of a gaseous discharge device regardless of variations in the initial filling pressure of the device.

These and other objects of this invention are attained in specific embodiments wherein the gaseous discharge device comprises a hollow cathode and a fine wire anode directed towards the hollow cathode so that the tip of the wire is the active portion of the anode and determines the anode-to-cathode spacing. The proportioning of the cathode, the anode-to-cathode gap, and the gas pressure may advantageously be such, as disclosed in Patent 2,804,565, M. A. Townsend, August 27, 1957, that the device exhibits a stable negative resistance characteristic over the range of currents and frequencies at which it is intended to be employed in the switching network.

An auxiliary aging anode is also positioned in the device. In accordance with one aspect of this invention, the main anode-to-cathode gap spacing is initially chosen smaller than the desired amount and the envelope of the device filled with gas and sealed off. A discharge is then initiated between the aging anode and the cathode; the aging anode is positioned to one side of the main gap so that it can readily see both the cathode and the main anode but its actual positioning is not critical. A fairly large discharge is initiated between this aging anode and the cathode, the hollow cathode structure being a copious source of electrons and positive ions. At the same time, the wire main anode is held at a negative potential with respect to the auxiliary anode; this may be by applying a negative potential directly to the main anode. Because of this potential at the main anode, positive ions issuing from the hollow cathode cause an intense bombardment of the end of the anode facing the cathode with a consequent etching or eroding action of the tip of the wire anode. By periodically interrupting the discharge and measuring the breakdown potential between the main anode and cathode, accurate track can be kept of the spacing between the anode and the cathode as the end of the anode is eroded away.

As mentioned above, for gap spacings larger than the spacing at the minimum in the Paschen curve, the gap breakdown voltage is a function of the spacing. Therefore by interrupting the discharge to the aging anode and measuring the breakdown voltage. the gap spacing may be readily determined. However, it should be noted that the gap spacing itself is only of importance as it determines the breakdown voltage; accordingly in accordance with a feature of this invention it is the final desired critical determination that is directly measured to ascertain when the gap spacing is correct. The initial variations in gas pressure are also compensated for. When the proper breakdown voltage is found, the discharge to the aging anode is not renewed and the eroding process stopped.

In accordance with another aspect of this invention, this process is entirely automatic. In one specific illustrative embodiment, the etching biases and the proper biases for breakdown of the main gap are alternately applied to the device under control of a relay operated by a clock source so that the aging discharge is periodically automatically interrupted to allow the breakdown biases to attempt to break down the main gap. The breakdown potential applied to the main anode at this time is chosen to be just above the desired breakdown voltage. This is done because, in this specific embodiment,

the main gap-will "break" down for --a-1l= "gap spacings smaller than that desired and, on breakdown of the main gap, the etching discharge will again be initiated and the anode further ionically' etched; Accordingly when the gap spacing is 'ust at"thedesired'breakdown' voltage, it is necessary that the n ain gap not break down-so that theperiodicetching' cycle is interrupted.

Actually because of'the change in gasdensity brought about 'y'by the temperature rise at the cathode; and the anode' duri-ng the high currentetchingprocess, the breakdown voltage which is measured during the interruption in the'efc-hing cycle; and 'thiis-within fafew hiilliseconds afterdhe etching is interrupted; fiS likelyi to be-several volts' lower than the 'br'eakdownfvoltage rif the 'tube when I it iSfCOl'd. Thisis to' beeirp ejctedfrom the'Paschencnrve 'wherein thehre'akdown "voltageis dependent on-both the anode-toeathodegap spai-ng ana-also- -the l gas pressure within that gapL I-Iowevq-r, hisditferencemaybe readily recognized and compensatedffor in determining the break- =down voltage-bias to -beapplied toithe main 'gap to determ ine 'whenthe etching process-should be interrupted.

Furtherg the cathode maybe suported bya bimetallic or 'other therrn'ally sensitive support so adjusted that the change in position of the cathode exactly compensates for the change in' density; as further =disclosed 'in-application sunris s-96, 13 1 ruse March 24, "19=5'5, r v. Holdaway; "Sucha mounting is particularly-advantageous injingsfbetween the anodes-and cathodes of all the devices havejbeen accurately determined to be the same in -ac- "cordance with the; techniques of this invention, still' the product for this one device will be lower and the-de- Vices breakdown volta'ge will-also lie-lower. This device will therefore not properly' cornpete in the operation of the network: forthefconnection heing set up.' In -accor-dance with the teaching ofthe above-'mentioned Holdaway application, the pd 'prcdnct niay' be kept'constant for all devices in the. network: under ,-.all operating conditions by supportingthe cathodeon a compensating'smoun't arranged :so' that heating. of'the ,cathode causes the. cathode tobe movedotheiexactxamount required to compensa'te ,for thelowering ofithe 'gas density in the anodeto-cathode gap, in addition tov originally, accurately determining theianodertomathode gaptspacing in accordance with this invention. i

' It is a featurefoflthis invntionithatthe spacingand thus the.brea'kdown voltage]betweenftheuanode"and cathode in a gaseous, disch r aaevk be determined by initiating agdischarge in me device andgbombarding' the :anode withpositive ions .to erode and etch away the end portion "of the anode.' T

It is another feature of this invention thatan auriiliary agingQanode is positioned in agaseous 'discharge'de'vice and a 'large. discharge initiated between theiauxiliary aging-anodevand thema'in cathode whilelthe potential of the main anode is maintained negativewithirespectfto they aukiliary. anode I so thatthe .main anode 'is f bombarded vby. pos'itiveionsi-from the Qagingldischarge ,tooetch away xthefend portion ofcthewdischarge. EurtherQin accordance wit h.;a .feature oiithis invention -lthe cathode .is advcan- .tageously :a. hollow (cathode ands ithus. a copionssonrce of .e1ectlmsiandn ezi n o -the;; 1 v =4 s anode is a wire anode with its end or tip facingthe holar a-am low of the cathode, the-critical spacing being determined 7 by the .end or tip of the wire anode and this end or tip being the portion etched or eroded away by the ion bombardment.

It is still another feature of this invention that the aging discharge be periodically interrupted to allow measurement of the anode-tc-cathode spacing;'-.Further,--it a feature of "this inventiorrqthatjtheranode-togcathode spacing be measured during the interruption of the aging discharge by determination of the breakdown voltagein the main gap. V a r It is a further feature of this invention that the auxiliary or aging/discharge :he periodically. interrupted; :and the main gap breakdown measuredd ltmg fllese'intervals, the

' aging discharge being nonreintiatedrwhen the spacing of the main gap has increased to the point that the main gap no longer breaks ,downon application of the applied breakdown potential. V a V p o It is a still further feature ofthis invention ;that aging apparatus include circuit rneans forscyclica'lly applying toithe aging anod e, main anode; and"'cathode"of the device either iappropriate-ibiases to maintain the aging discharge and ionical-ly etch the main anode or appropriate biases to attempt to'hreak down the main gap-nnderza constant breakdown ijpotentia-l across thegap; the circuit being mangedsothat'the application of'the: biases to' "the" electrodes for' etching of the anode is discontinued on failure of =-the;mai-n 'gap to breakdown under the constant breakdown-potential.

=- A complete understanding.of-these:andwarionsnther features of this invention can -:be gained .from consideration of -the tollowing :detailedrlescriptionsand the accomrpanying drawing-, in w vhich: 7

- Fig; 1 is a schematic representation of: one' circuitemr ployable in -carrying-out 'theaprocess of ;this invention;

Fig. 2 is a perspective view of an illustrativegaseous discharge :device; which-smay: befifabricated ,inzaccordance with this ;invention,-; a portion; of;iheiglass;.zenvelopeihaving been brokeneawayeto show .:the Einternalaelectrodcs more clearly;- -and a i Fig. 3 .is a schematic representatiion' of. one, illustrative embodiment of agingdapparatuscin accordancewith this a V zpositiveiionsl :In this specific embodiment the athode 1'1 .is1mounted.=gby.n :support; wire 5:14,} though bimetallic supports-or JILOHBIS, aszfurtheradisclosed injapplicationaserial No: 49.6,411gifi16iM21ICli124, 1-955;of V. L.- Heldaway rand :re'ferred;-to.. aboye;:may,also-advantageously be eruiployed.

iiThei mode'liyis 1a fine (or 1 thin-wire supported :from asleuger wire lsasoathatthetip-of the wire 12;is' directed towards and opposite the hollow cathode 11. Advan- -tageously the wire anode 12 is; axiallyw mounted with :respect tolthe cathodel-l SCkflJEI the etchingof thetip-of the wire 12, as further described-1 below, will be sym- :metric. J

aging anodes 17,.--is also; mounted "within the;envelo,pe-110, as by aa'ileadwire. 18. 1AI10d6:11=iSlfld -vantafgeouslyy positioned;v to :one side of the I main anodecathode gap-and in suchrrelationi .theretothat it can ,.direjctly seelboth gtheernain ganodeandthe cathode; .-A,spot of radium 20 may also adnantagennsly hepositionedDn -thein'side;of;the envelope 10, as is ;4known;in1the art,

fLhe critical; spacing and :the spacing -.th3t1is accurately and automatically,determinedsintaccordancewithsthis in- ;vention is the. anodedo-cathode gap, ndesignated --;by';,the

tozthe drawing, the :gaseous dischargeldelsee ers made too small when the device is assembled, filled with gas at an appropriate pressure, and seeded off. A discharge is then initiated between the aging anode 17 and the cathode 11 by the voltage source 23 connected therebetween. At the same time a negative potential, from the voltage source 24, may advantageously be applied to the main anode. Meters 25 and ballast resistances 26 are included in the connections to both the cathode 11 and the anode 12; the ballast resistances 26 limit the discharge current to the desired values which may be readily ascertained by the meters 25. The correct value of current to be utilized in the anode etching process for any given device configuration will be determined by that configuration, the spacings, the type and shape of the electrodes, and the rapidity with which it is desired that the etching progress. In one specific illustrative embodiment I have found that satisfactory etching of the anode 12 by ionic bombardment can be realized by drawing about 30 milliamperes to the cathode 11 and to milliamperes to the anode 12. In this specific embodiment the gap spacing 22 was increased from 0.015 inch to 0.025 inch in forty minutes by ionic etching in accordance with this invention.

In this one specific illustrative embodiment the anode 12 was of 0.005 inch molybdenum wire and the anode 17 of 0.020 inch molybdenum wire. The anode 12 was located centrally with respect to the opening of cathode 11 and initially 0.015 inch away therefrom; the anode 17 was located so as to be level with the top of the cathode 11 and 0.030 inch away therefrom, though the positioning of the auxiliary anode is not critical.

Turning now to Fig. 3, there is depicted one illustrative embodiment of apparatus, in accordance with this invention, for ionically etching the anode 12 and cyclically interrupting the aging discharge and the ionic etching to measure the breakdown voltage of the main gap and thus the main gap spacing. The cathode 11, main anode 12, and aging anode 17 are each connected to the armatures 30, 31, and 32 of a relay having an actuating coil 33; a fourth armature 34 is connected to a source of positive potential 35. When it is desired to start the etching process, a switch 37 is manually closed, closing a circuit from ground through the coil 33, switch 37, and a clock switch 38 to a source 39 of negative potential. The clock switch is opened and closed in accordance with a predetermined cycle, which in one specific embodiment was closed for 70 seconds and opened for 10 seconds. Clock switch 38 may be controlled by any type of synchronous or clock source; in the specific embodiment depicted in the drawing the openings and closings of the clock switch 33 have been indicated as controlled by a rotating cam 40 under control of a clock or synchronous motor 41.

When the switch 37 is closed during that portion of the clock cycle that the clock switch 38 is closed, relay 33 is actuated transferring each of the armatures 30, 31, 32, and 33 to the lower contacts 43,' 44, 45, and 46, respectively. Closure of the armature 34 and contact 46 applies the source 35 to the relay 48, thereby closing con tacts 49. An alternate path is now provided between the relay 33 and the source 39 and the switch 37 may be released.

Operation of the relay 33 has also applied appropriate potentials to the aging anode 17, main anode 12, and cathode 11 to initiate the etching discharge between the cathode 11 and the anode 17 and to bombard the anode 12 with ions to cause an etching or eroding of the tip of the anode 12 to increase the spacing of the main gap. Thus the positive terminal of source 51 is connected through contact 45 and armature 32 to the aging anode 17, the negative terminal of source 51 being connected to ground; at the same time cathode 11 is connected through armature 31 and contact 44 to ground through a ballast resistance 52 and a meter 53. Similarly the main anode 12 is connected through the armature and the conl??? 43 to a n h o gh a ballast resi tance 52 an meter 53. While I have found that the anode 12 may advantageously be connected during the ionic bombardment to a source of negative potential, this is not essential provided that the main anode is negative with respect to the auxiliary anode during the etching process so that it will be bombarded by ions. Further, the current drop across the resistor 52 serves to apply a negative bias to the main anode. However, the resistor 52 mainly serves to limit the current flow and thus limit the rapidity of the etching process.

With the relay 33 operated and the various armatures in the positions described above, the etching process continues for the remainder of the closed portion of the clock cycle of clock switch 38 which, in one illustrative embodiment, is for the remainder of the 70 seconds. At the end of this interval the clock switch 33 opens, there by releasing the relay 33, interrupting the etching discharge in the device, and removing the source 35 from the relay 48. During the open portion of the clock cycle, which in this one illustrative embodiment is 10 seconds, the device is allowed to cool down.

At the end of the open port1on of the clock cycle the switch 38 closes again. As neither switch 37 nor contacts 49 are closed, the relay 33 is not activated and the etching process does not recommence. However, current is applied to the winding of a relay 54 closing the contacts :5 and thus applying a positive potential, from the priorly set breakdown voltage source 56, through the contact 57 and armature 30 to the anode 12. At the same time both the cathode 11 and the auxiliary anode 17 are connected to ground through the armatures 31, 32 and contacts 58, 59, respectively, and the ballast resistance 60.

If the tip of the main anode 12 has not been sufliciently etched away, so that the breakdown voltage of the device is still less than that desired, the device will break down when the breakdown voltage is applied from source 56 to the main anode 12. Accordingly current will flow to the cathode 11 and through the resistance 60 to ground, causing a pulse of voltage to pass through a capacitor 62 connected to the resistance 60 and to the starter anode 63 of a gaseous triode 64. This voltage pulse triggers the gaseous triode 64 which fires and current flows in its main gap. This current also flows through the winding 4's causing the contacts 49 to close, thereby again operating the relay 33. As before, operation of relay 33 transfers each of the armatures 30, 31, and 32 from the voltage breakdown measuring circuit to the appropriate biases and connections for further etching of the anode 12. At the same time closure of the contact 46 and armature 34 again applies the source 35 to the relay 48.

The gaseous triode 64 is thus no longer necessary and conduction therein is put out by a relaxation effect due to the inductor 65 and capacitor 66 connected to the anode 67 of the triode 64. The triode is of course advantageously extinguished before the next opening of the clock switch 38.

For the remainder of the closed portion of the clock switch cycle the etching of the anode 12 continues. When the clock switch 38 again opens, the device 10 is again allowed to cool down before applying the breakdown voltage from source 56 through the contacts 55 to the device on the next closure of the clock switch 38. The above cycle of operation continues until the tip of the anode 12 has been ionically etched away sufliciently so that the predetermined breakdown voltage from the source 56 is insufiicient to efiect a discharge between the anode 12 and cathode 11. When this occurs triode 64 will not conduct and the contacts 49 will remain open, thereby ending the etching process.

It is to be understood that this invention is not dependent on the type of cathode, the electrode configuration, or the gas pressure in the device. While a helically coiled cathode has been depicted in the drawing for purposes ot illust ation, any other type of cathode capable btlsnstaininata are.antigensinsulating.

-ZVarithesei other nathnde a s disclo e. i th sa oreanaenticned:Iewn end;patent;pbu t sinvcn n i not limited t-tc; merelxt heza hndcs disclo e there t It is -to,.b emphas ze a a n that, h l n desathod agan 1s. accuratelyad t rmined. lna cord n c w th oy; invention,i it is like breakdown voltage itself that iis 9 pa amount int rest, Ihuswhen a num er-of d vice such as that disclosed in Fig. 2, are fabricatedand have their gani na ings det rmined inaccordance with my-in- ,ventipn, it is possibleth th :IpeC iYegaPpaing wi l not be the same t ;thefilling pressnre th gas rinlhe yarious devices manbeslightly different-; 1 owev r, the e difi rences; arcaalso compens ed o s it is th final and important cr ter onathe. reakdown.voltsge i sel w ch determines whenithe gap spacing is proper.

Thus. i is .to be undcrstoodthat the above-d scrib d arran me t ar fllustrafive of the ppl ation of th Qrinciplesof: theinvention c-Nnnierous other arrange, V

ments may be devised by, those s killed in the art without,departing' from thespiritand scope of the invention.

' What, is ;claimed is:

7 1., In the, fabrication; of gaseous di'scharge devices, the methods. of accurately determining the anode-to-cathode breakdown voltage comprising initiating-1a first discharge in the device,maintainingIthe anode at a potential to be b on'ibarded byv ions frornsaid firs't dimharge to etchaway the end portion of v the; anode; periodically, interrupting said firstadiscliarge, :attemptingto; establish a discharge between saidanode and cathodewhile. said first discharge .is interrnpted, ,,and permanently:discontinuing said first discharge when said discharge" between the anodeand cathode, cannot belestablished. 7 g g ,2. Apparatus for accurately: determining the spacing between Qthe anode-1 andtcathode :of a gaseous discharge device having another, electrode comprising. means i for initiating a discharge between said cathode and said ,other electrode, means fornlaintainiugnsaid.anode at; a potentialtto be bombarded by 10. 15 f omestaid discharge, means for.v periodically interrupting said, cathodel-torother telec- ,trodedischargg means for establishing; a discharge between saidcathodejand anode while said other discharge .is interrupted, and means forpe manen ly i c n in in said'cathode-toeother electrodeidischarge when the anodeto-ca'thodeibreakdownv voltage' -c has, attained .a desired value" a I 1 3; Apparatus f rAaccura elytaius ing he spacin tw ntthe, anode and catho e ofjagga ous discharged:- vice comprising means or nitia ing. a, fi d char ei said device, means for maintaining, theanode at a poten- -.-tial sufiicient to. cause. ion bombardment a fvsaidanc e y said Y discha g .rneans fo pe d cal y int rr p in ai discharge,:means .for attempting to, initiate a. discharge between said anode and cathode when said first discharge is interrupted, and means for reinitiating saidmfirst discharge on occurrence of said discharge between said ,anodcand said cathode.

4...-APParatus for accurately adjustingthe breakdown voltage betweenrthc vanode. and, cath d of a gas ous di chargeIdevicecomprising means f0!vv alternately applying a firstiand, asecond set of potentials; toasaid anode and cathode: said first set of potentials establishing" first discharge, in saiddeviceand maintaining said anode at Lav potential such. that it is subjected; to ion bombardment and said second setofpotentials applying a positive po- ,tential to said anode. and .sceking to establish a discharge between said anode and,said cathode, and means for interrupting said alternate pplication of, said first and second sets of potentials when said second 5610i potentials 7 can no longer establish said discharge between said anode and-'said-cathode. V

= 5.;Apparatus Y for accurately determining the spacing I abetween the anode-and cathodeof a gaseous discharge device having-a third electrode comprising means forinitimting' a first -dischargesbetween said cathode and saidthird E e ec ro e-im mi rgapplying aipo cntialrtcs aid an; suc tt ats n e j je t to iunbqmba d t o tdischal eaga u- 7 6, Annal ftus r amuatdvnetermn ng thc-s'paciugbetween h an deand,cat de fi aa a enu ar ede vice a ,haringca sa xiliary a de :ccinpr w 5m" lter at y 'npl ta firstgscto ro i V anddecc thqdcaandauX' a zancdet rm n ainia u cha ge between s id; mode and: said. aux ia y and 'bcmb dlsaidan idld to etch, aw an en se o p01 v ofle e s harg th reibe we nna d mea s fo cea in sa a ma e-ap l cat c n a 'firttau s condf t of 'p enti s whensaid econ t o po als canQ QlQu er 'a firsfiset of contacts closed to 'said'armatures when said relay is activated, meansap plying a breakdown potential "to said anodegto attemptto effect a discharge between said anode and "saidcathode, 'saidi last-mentioned means including a-sec0nd'setof contacts closed to-said armature when; saidrelayis; not activated, a clock" source for activati'ng said-'relay to transfer; said armature; between said first and said-second sets:of contacts in; accordance with a -predeter-mined cycle, and means for connecting said 'cl'ocksource to-said relay -on occurrence of ajdischarge bet-weensaid -anode and said cathode; g V

8; Apparatus -i11-'8. 660fd3fl6' with claim "'7 further: comprising means forapply-ingsaid breakdown -potential to said anode only during-"the activating portion of said cycle a 9. Apparatns inaccordance with; claim -8-wherein said connecting means iorther -eomprises; a; gaseous triode having a starten anode; cathode, ;andf main anode, means applyinga voltage to-said starter anode on oceurrence 'of said discharge, and relay means activated o'rr-flowof current in'said triode-for-connecting said clock source to saidfirst-mentionedrelaymeans a 10. Inthe fabricationofgaseous-discharge devices,-the

l method nf-accurately determining the anode-to-cathode breakdown voltage of adevice-comprising--initiating a discharge between theacathode and a third electrode in the device; tl'ierebybombardingthe anode with-positivevions to erode and etch away the end portion thereof, periodically interrupting the discharge between the cathode-and the third electrode, and seeking, during the period t of 1a- -terrupt-ion, to; establish a discharge between the cathode and the anode -by apply i-ngtherebetween a preassi-gned voltage, whereby the anode-to-cathode breakdown volt- 1 age is accurately determined when the -preassignedwoltage cannot effect a brea kdoWn therebetween;

l1. inghcafabricationofgaseous di-scharge devices; the .methodaof accurately determining 'theanode-to-cathode 'breakdown-Mol-ta ge comprising initiating-a-firstdischarge between the cathode and anotherelectrode in --the' deyic e,

- maintainingthefanode at a negative-potential With-respect to said other electrode,-' -'-thereby bpmbardingithe; anode v-witbpositi-ve ions to-etch away the end portion thereoi,

an. asanaabaana anneal a in 9 periodically interrupting the first discharge, attempting to establish a discharge between the anode and cathode While the first discharge is interrupted, and permanently discontinuing the first discharge when the discharge between the anode and cathode cannot be established.

12. In the fabrication of gaseous discharge devices, the method of accurately determining the anode-to-cathode spacing comprising the steps of initiating a discharge be tween the cathode and an auxiliary anode, thereby etching away the end portion of the anode, periodically interrupting the discharge between the cathode and auxiliary anode, attempting to establish, with a preassigned voltage, a discharge between the cathode and anode while the cathode-to-auxiliary anode discharge is extinguished, and discontinuing the cathode-to-auxiliary anode discharges when a cathode-to-anode discharge cannot be established.

13. In the fabrication of gaseous discharge devices, the

method of determining accurately the anode-to-cathode breakdown voltage of a device having a hollow cathode, a wire anode including an end portion adjacent to and pointed at the hollow of said cathode, and another electrode, comprising the steps of initiating a first discharge between said cathode and said other electrode, maintaining said anode at a potential to cause an intense ion bombardment of the end thereof facing said cathode, periodically interrupting said first discharge, seeking to establish, with a preassigned voltage, a second discharge between said cathode and anode, and permanently discontinuing said first discharge when said second discharge cannot be established.

Beggs Oct. 7, 1947 Depp May 16, 1950 

